Heat is often created as a byproduct of industrial processes where flowing streams of liquids, solids, or gasses containing heat must be exhausted into the environment or otherwise removed in some way in an effort to regulate the operating temperatures of the industrial process equipment. The industrial process oftentimes uses heat exchangers to capture the heat and recycle it back into the process via other process streams. Other times it is not feasible to capture and recycle the heat because it is either too hot or it may contain insufficient mass flow. This heat is referred to as “waste” heat and is typically discharged directly into the environment or indirectly through a cooling medium, such as water or air.
Waste heat can be converted into useful work by a variety of turbine generator systems that employ well-known thermodynamic cycles, such as the Rankine cycle. These thermodynamic methods are typically steam-based processes where the waste heat is recovered and used to generate steam from water in a boiler in order to drive a corresponding turbine. Organic Rankine cycles replace the water with a lower boiling-point working fluid, such as a light hydrocarbon like propane or butane, or a HCFC (e.g., R245fa) fluid. More recently, however, and in view of issues such as thermal instability, toxicity, or flammability of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate more greenhouse-friendly and/or neutral working fluids, such as carbon dioxide (CO2) or ammonia.
The efficiency of a thermodynamic cycle is largely dependent on the pressure ratio achieved across the system expander (or turbine). As this pressure ratio increases, so does the efficiency of the cycle. One way to alter the pressure ratio is to manipulate the temperature of the working fluid in the thermodynamic cycle, especially at the suction inlet of the cycle pump (or compressor). Heat exchangers, such as condensers, are typically used for this purpose, but conventional condensers are directly limited by the temperature of the cooling medium being circulated therein, which is frequently ambient air or water.
On hot days, when the temperature of the cooling medium is heightened, condensing the working fluid with a conventional condenser can be problematic. This is especially challenging in thermodynamic cycles having a working fluid with a critical temperature that is lower than the ambient temperature. As a result, the condenser can no longer condense the working fluid, and cycle efficiency inevitably suffers.
Accordingly, there exists a need in the art for a thermodynamic cycle that can efficiently and effectively operate with a working fluid that does not condense on hot days, thereby increasing thermodynamic cycle power output derived from not only waste heat but also from a wide range of other thermal sources.